The Department of Homeland Security has spent billions since 9/11 trying to keep dangerous people and dangerous explosives off airplanes, and treating us all air travelers like potential terrorists in the process. But according to a former security adviser to a leading airline, the terrorists have changed the game — and the government hasn’t yet caught on.

According to Ben Brandt, a former adviser to Delta, the airlines and the feds should be less concerned with what gels your aunt puts in her carry-on, and more concerned about lax screening for terrorist sympathizers among the airlines’ own work force. They should be worried about terrorists shipping their bombs in air cargo. And they should be worried about terrorists shooting or bombing airports without ever crossing the security gates.

Brandt says aviation security needs a fundamental overhaul. Not only is the aviation industry failing to keep up with the new terrorist tactics, TSA’s regimen of scanning and groping is causing a public backlash. “From the public’s perspective, this kind of refocusing would reduce the amount of screening they have to put up with in the United States,” Brandt tells Danger Room, “and refocus it where it’s needed.”

In the new issue of the CTC Sentinel, a wonky security newsletter published by West Point’s Combating Terrorism Center, Brandt all but indicts his former industry and its government protectors. “Government regulators suffer from a lack of imagination in anticipating and mitigating emergent and existing threats” to air travel, he writes.

Think first about what aviation security is. Since 9/11, it’s largely been a line of defense ahead of a departure gate to keep dangerous people and dangerous materials off a plane. By Brandt’s calculations, it’s cost $56 billion since 9/11. In one sense, it’s worked as planned: No planes have been blown up or hijacked for a decade.

But the last several years’ worth of plots on the friendly skies indicate the terrorists have switched their game plans. In January, a suicide bomber didn’t try to board a plane at Moscow’s Domodedovo airport. He detonated before going through security, in the crowded entranceway, killing 35 people and wounding over 150 more. Last fall, al-Qaida’s Yemen branch skipped the boarding call and shipped bombs packed in printer cartridges back to the States.

Less conspicuously, terrorists have started to infiltrate the airlines and airports themselves. Rajib Karim, for instance, worked as an IT specialist for British Airways. But inspired by al-Qaida YouTube preacher Anwar al-Awlaki, Karim offered to help al-Qaida sneak bombs aboard planes at London’s Heathrow airport, and claimed to have support from sympathetic airport workers. The airlines and airports barely conduct employee background checks, Brandt claims — and of course, none of those employees need to go through a “porno scanner,” get a pat-down or have their luggage rifled through.

Speaking of those scanners: We all remember how on Christmas Day 2009, Umar Farouk Abdulmutallab packed explosives into his underwear and headed on a flight to Detroit. That plot that failed only because of Abdulmutallab’s inability to light himself on fire. That’s how we got the invasive new scanners, which seek to catch the explosives or components that traditional metal detectors miss. But Brandt says they’re not so great: They “detect only two popular explosive compounds,” he writes. (He declines to name them in the interest of public safety; the Department of Homeland Security opted not to comment on Brandt.) Explosives detection equipment “is also not designed to detect the components of improvised incendiary devices (IIDs), making the use of these correspondingly attractive to terrorists.”

TSA is trying to get away from its stigma of being the guys who grope and photograph you. It’s taking the porno out of the scanners by getting rid of the “nude” imaging displays. Its director, John Pistole, talks about becoming an “intelligence driven” agency that compiles behavioral profiles of potential terrorists and — someday — targeting its toughest screening on only those who fit the profile. Kids no longer have to take their shoes off before boarding a plane.

Just one problem, according to Brandt: The behavioral science is no panacea. “The scientific community is divided as to whether behavioral detection of terrorists is viable,” he writes. According to the Government Accountability Office, TSA put together a behavioral profiling program “without first validating the scientific basis for identifying suspicious passengers in an airport environment.” Even if the science was sound, the office found last year, TSA officers “lack a mechanism to input data on suspicious passengers into a database used by TSA analysts and also lack a means to obtain information from the Transportation System Operations Center on a timely basis.”

Pistole talks about creating a “robust and multi-layered system” of defense, in case a certain measure fails. That’s a worthy effort, but it needs even more layers, Brandt argues. Abdulmutallab boarded his flight in Amsterdam — taking advantage of its relatively lax security, a harbinger of threats to come. ”Given that most aviation-focused attacks are likely to originate outside the U.S., it would seem to make more sense to upgrade screening for U.S. airline operations at those airports,” Brandt says.

None of this is going to be easy, or cheap. Brandt proposes that the government subsidize airlines for better employee background checks or explosives detection tech. But that’s could strike taxpayers as a bailout.

On the other hand, he and Pistole actually share the same headspace, so it’s possible that TSA will buy his overall critique. “The best defense is still developing solid intelligence on terrorist groups interested in targeting aviation,” Brandt says. Beats treating us all like terrorists.

Photo: Flickr/Inha Leex Hale